This invention relates to a solid golf ball and more particularly, to a solid golf ball comprising a solid core and a cover wherein a cover stock is loaded with an inorganic filler for improving the durability against cracking of the cover.
In the prior art, attempts were made to soften golf balls for the purpose of improving the resilience and xe2x80x9cfeelxe2x80x9d of golf balls. One common approach involves softening the core from the standpoint of feel and enclosing the soft core within a hard cover to compensate for resilience. This approach is successful in improving resilience, but leaves the problem that the cover can be cracked upon repetitive shots.
The addition of inorganic fillers to cover stock is known from a number of patents, for example, JP-B 5-73427, JP-A 57-25867, JP-A 60-210272, and JP-A 6-277312. The addition of inorganic fillers is to increase the specific gravity of the cover for increasing the moment of inertia of the ball for improving the flight performance thereof. Excess loading of inorganic filler can however compromise the resilience and cracking durability of the ball.
An object of the invention is to provide a novel and improved solid golf ball in which an appropriate amount of an inorganic filler is added to a cover stock as a reinforcement so that the cover is drastically improved in durability against cracking by repetitive shots.
The inventor has found that when an appropriate amount of an inorganic filler having an optimum specific gravity is added to a cover stock, the inorganic filler advantageously functions as a reinforcement for improving durability against cracking. As a result, a golf ball comprising a soft core and a hard cover in a combination which has never been established heretofore is obtained.
The invention provides a solid golf ball comprising a solid core and a cover enclosing the core. The solid core undergoes a deflection of 3.0 to 5.5 mm under a load of 100 kg. The cover is formed of a thermoplastic resin-base cover stock in which a particulate inorganic filler, preferably having a specific gravity of up to 4.8, is uniformly dispersed in an amount of at least 11 parts by weight, preferably 11 to 45 parts by weight, per 100 parts by weight of the cover stock. Quite unexpectedly, this inorganic filler exerts the excellent reinforcing effect of restraining the cover from cracking by repetitive shots. There is obtained a softened golf ball based on a soft core/hard cover combination which has never been established heretofore and having improved resilience and a pleasant feel.
It is understood that although the invention adds an inorganic filler to a cover stock, the invention does not intend to increase the specific gravity of the cover for increasing the moment of inertia of the ball for improving the flight performance thereof. Rather, by dispersing in a cover stock an appropriate amount of an inorganic filler having a certain mean particle size and specific gravity, the invention intends to cause the inorganic filler to function as a reinforcement for improving the durability against cracking of the cover, thereby achieving a softened golf ball based on a soft core/hard cover combination which has never been established heretofore.